What is the best way to insulate the exterior of a post and beam timber frame with rigid insulation?

Ron Busch

Building a 24 X 50 Post and Beam Barn.  Planning to insulate on the exterior with no interior insulation as I wish to keep the bones of the barn exposed internally.  Wall currently has 3/4" Shiplap pine sheathing over the Girts.  Looking at emplacing 4" R20 Rigid XPS Panels seam taped. Those would be strapped to the wall with 7 1/2" screws into the Girts. Board and Batten siding would be placed on top (min 1" to 2" air gap behind the Board and Batten).  Barn will be heated by radiant floor heat. Will this type of insulation work?  Do I need to place a vapour or air barrior on top of the 3/4" Shiplap Pine prior to emplacing the Rigid Panels?  Do I need to place a Tyvek type sheathing over the insulation between it and the Board and Batten?

Thank you


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